Effect of Tension Stiffening on Torsional Behaviour of Square RC Columns

Abstract

Codes specify high factory of safety in design to prevent brittle torsional failure of reinforced concrete (RC) columns. This necessitates accurate prediction of the torsional behavior for efficient design of these members. However, very few analytical models are available to predict the response of RC members under torsional load condition. Softened truss model (STM) developed in the University of Houston is one of them, which is widely used for this purpose. The present study shows that STM prediction is not sufficiently accurate particularly in the post cracking region when compared to test results. It also aims at developing an improved analytical model for RC square members under torsional load conditions. Since concrete is weak in tension, its contribution to torsional capacity of RC members was neglected in the original STM. The present investigation revealed that, disregard to tensile strength of concrete is the main reason behind the discrepancies in the STM predictions. The original STM has been extended in this study to include the effect of tension stiffening (TS) to get an improved prediction of torsional behaviour of RC members. Three different tension stiffening models have been considered in this paper. The efficiencies of the models were calibrated through comparison with test data on local and global behaviours. The exponential tension stiffening model is found to give more accurate predictions.